Abstract
Listeria monocytogenes is an important Gram-positive foodborne pathogen. However, limited information is available on the comprehensive investigation and potential risk of L. monocytogenes in fresh aquatic products, which are popular to consumers in China. This study aimed to determine the occurrence, virulence profiles, and population diversity of L. monocytogenes isolated from aquatic products in China. In total, 846 aquatic product samples were collected between July 2011 and April 2016 from 43 cities in China. Approximately 7.92% (67/846) aquatic product samples were positive for L. monocytogenes, 86.57% positive samples ranged from 0.3 to 10 MPN/g, whereas 5.97% showed over 110 MPN/g by the Most Probable Number method, which included two samples of products intended to be eaten raw. Serogroups I.1 (serotype 1/2a), I.2 (serotype 1/2b), and III (serotype 4c) were the predominant serogroups isolated, whereas serogroup II.1 (serotype 4b) was detected at much lower frequencies. Examination of antibacterial resistance showed that nine antibacterial resistance profiles were exhibited in 72 isolates, a high level susceptibility of 16 tested antibiotics against L. monocytogenes were observed, indicating these common antibacterial agents are still effective for treating L. monocytogenes infection. Multilocus sequence typing revealed that ST299, ST87, and ST8 are predominant in aquatic products, indicating that the rare ST299 (serotype 4c) may have a special ecological niche in aquatic products and associated environments. Except llsX and ptsA, the 72 isolates harbor nine virulence genes (prfA, actA, hly, plcA, plcB, iap, mpl, inlA, and inlB), premature stop codons (PMSCs) in inlA were found in four isolates, three of which belonged to ST9. A novel PMSC was found in 2929-1LM with a nonsense mutation at position 1605 (TGG→TGA). All ST87 isolates harbored the ptsA gene, whereas 8 isolates (11.11%) carried the llsX gene, and mainly belonged to ST1, ST3, ST308, ST323, ST330, and ST619. Taken together, these results first reported potential virulent L. monocytogenes isolates (ST8 and ST87) were predominant in aquatic products which may have implications for public health in China. It is thus necessary to perform continuous surveillance for L. monocytogenes in aquatic products in China.
Highlights
Listeria monocytogenes is an important foodborne pathogen worldwide, that can cause life-threatening listeriosis disease in vulnerable groups including pregnant women, fetuses, elderly people, and immunocompromised individuals, with a considerable mortality rate (20–30%) (Lomonaco et al, 2009)
The contamination level by L. monocytogenes in aquatic products was determined by the most probable number (MPN) method
Of fresh aquatic products samples, which are popular among consumers in China, approximately 7.92% were positive for L. monocytogenes
Summary
Listeria monocytogenes is an important foodborne pathogen worldwide, that can cause life-threatening listeriosis disease in vulnerable groups including pregnant women, fetuses, elderly people, and immunocompromised individuals, with a considerable mortality rate (20–30%) (Lomonaco et al, 2009). Listeriosis diseases have been increasingly reported in China annually, especially in developed cities (Wang et al, 2015, 2018) This trend may be linked to the trend of direct consumption of fresh foods and ready-to-eat foods in China, especially in developed cities. According to data compiled by the National Bureau of Statistics of China, the average consumption of aquatic products per capita has increased annually and in 2016, it was 11.4 kg. According to data compiled by the National Bureau of Statistics of China, the average consumption of aquatic products per capita has increased annually and in 2016, it was 11.4 kg1 In this context, it is necessary to systematically investigate the contamination level of L. monocytogenes in aquatic products in China
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